JP3059286B2 - Display device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a driving method using a liquid crystal display element such as a display panel using a ferroelectric liquid crystal, and more particularly to an improvement in the visibility of a moving image of a ferroelectric liquid crystal display element. The present invention relates to a display device and a driving method.

[0002]

2. Description of the Related Art Conventionally, a refresh scan type CRT is mainly used as a display device as a computer terminal device, and a frame frequency of 60 Hz or more is used in order to prevent flicker (screen flicker). In order to improve the visibility of the movement display of the inside information (movement of a mouse, an icon or the like), a non-interlace method is adopted. For this reason, this CRT requires higher power as the display resolution becomes higher, and the drive control device becomes larger, resulting in higher cost. Note that a TV employs a 1/2 interlace system with a field frequency of 60 Hz and a frame frequency of 30 Hz from the viewpoint of displaying moving images and simplifying the drive control system.

In recent years, flat panel displays have attracted attention due to the inconvenience of increasing the size and power of CRTs.

At present, there are several types of flat panel displays. For example, the twisted nematic liquid crystal high time division method (STN), the modification of black and white display (NTN), and the plasma display method use the same method as the CRT as the image data transfer method. The screen changing method also employs a non-interlace method with a frame frequency of 60 Hz or more. The reason for this is that these display panels do not have a memory property in terms of display principle, and therefore require a refresh cycle of a frame frequency of 60 Hz or more from the viewpoint of flicker prevention. Also, in a method (TFT, MIM, TFD method, etc.) in which a switching transistor or a non-linear element is formed in each pixel of the twisted nematic liquid crystal, image information can be held within one frame at the maximum. As in each system, a refresh cycle of 60 Hz or more is required.

On the other hand, the ferroelectric liquid crystal display device has a feature of being able to hold image information once displayed (memory property), and therefore has a large screen and high definition display far exceeding the above-mentioned various display devices. Is possible.

[0006]

However, in such a ferroelectric liquid crystal display device, when the display panel has a large screen, the frame frequency inevitably decreases, and as a result, the visibility of a moving image in particular decreases. There was a problem.

As a method for solving the above-mentioned problem, a driving condition for shortening a one-line scanning time, that is, a driving voltage Vo
It is conceivable to increase the frame frequency by increasing p. On the other hand, when the ferroelectric liquid crystal display panel is driven for a long time, the frame display area outside the information display area (hereinafter, referred to as a frame display section) As described above, there is a phenomenon that liquid crystal molecules move in a region where a fixed pattern is displayed. The movement phenomenon of the liquid crystal molecules greatly depends on the driving voltage Vop.
The higher the value is, the more remarkable the movement phenomenon becomes. Therefore, there is a disadvantage that Vop cannot be increased in terms of durability performance. As a response to the movement of the liquid crystal molecules, a driving method that makes use of the characteristics of the ferroelectric liquid crystal and refreshes only when updating the screen and sets the memory state when not updating is conceivable, but since the memory property of the liquid crystal element is not semi-permanent, This causes a new problem in image quality.

As described above, with the increase in the screen size of the display panel, there has been a problem that it is not possible to simultaneously satisfy both characteristics of the visibility and durability of a moving image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has a display device and a driving method for achieving both visibility and durability of a moving image displayed on a ferroelectric liquid crystal display element. The purpose is to provide.

[0010]

In order to achieve the above object, the present invention firstly provides a display device having a ferroelectric liquid crystal display element and a driving means for driving the liquid crystal display element. Detecting means for detecting that the image information to be displayed on the liquid crystal display element has been changed; and changing the image information to be displayed on the liquid crystal display element in accordance with the detection result from the detecting means. , So that the frame frequency is higher than when no change is made to the image information,
Means for changing a driving condition of the liquid crystal display element, and secondly, a display apparatus having a ferroelectric liquid crystal display element and a driving means for driving the liquid crystal display element. A driving method, comprising detecting that a change has been made to image information to be displayed on the liquid crystal display element, changing a frame frequency according to the detection result, and changing the image information to be displayed on the liquid crystal display element. The driving condition is changed so that the frame frequency becomes higher when the change is made, and when the image information is not changed, the frame frequency is lower than when the image information is changed. A driving method of a display device characterized by changing driving conditions as follows.

[0011]

In a preferred embodiment of the present invention, two types of the frame frequency are prepared, and after detecting that a change has been made to the image information to be displayed on the display element, the frame frequency is transmitted to the liquid crystal display element. The liquid crystal display device is driven at the higher frame frequency only in the frame until the displayed image is updated to the image after the change, and is driven at the lower frame frequency otherwise.

[0013]

According to the present invention, a display panel comprising a ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having a matrix electrode formed of a scanning electrode and an information electrode is driven. In this case, it is possible to detect that the image information to be displayed on the display panel has been changed, and to control the driving conditions of the display panel according to the detection result.

That is, when the image information is not changed, the driving is performed at a low frame frequency so that the driving voltage Vop is low in consideration of durability, and when the image information is changed, The driving is performed by increasing the driving voltage Vop so as to obtain a high frame frequency in consideration of visibility.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a liquid crystal display device according to one embodiment of the present invention. In Figure 1, 1 is the scanning electrode S ₁ as shown in FIG. 2, S _2, ‥‥, S glass substrate formed with _m and data electrodes I _1, I _2, ‥‥, glass formed a I _n A ferroelectric liquid crystal display element in which ferroelectric liquid crystal is sandwiched between a pair of substrates 11 and 11 with a substrate, 2 is a driver IC board for driving scanning electrodes, and 3 is a driver IC board for driving information electrodes. . In the liquid crystal display element 1, reference numeral 12 denotes a sealing portion, 13 denotes a sealing portion, 14 denotes an information display area, and 15 denotes a frame display area.

The specifications of the liquid crystal display element (liquid crystal panel) 1 are shown below. Number of information display pixels: 480 (number of scanning electrodes) × 640 (number of information electrodes) (In the electrode plan view of FIG. 2, m = 480, n = 64
0) Liquid crystal: pyrimidine-based liquid crystal Phase change As shown in Table 1.

[0018]

Table 2.8 ℃ 60.0 ℃ 79.7 ℃ 86.1 ℃ Cryst ⇒ SmC * ⇒ SmA ⇒ Ch ⇒ Iso Spontaneous polarization (Ps) 4.8 nc / cm ² (40 ℃) Cell thickness (pair) (Interval between the substrates): 1.2 μm Alignment treatment A rubbing treatment was performed on the polyimide film provided on the pair of substrates 11 and 11 (see FIG. 1), and their directions were parallel to each other. The rubbing direction was parallel to the scanning electrode. In FIG. 1, an arrow A indicates a rubbing direction.

The above-mentioned liquid crystal display device is driven by a 15-row scanning method (1/1/0) using the driving waveform voltage shown in FIG.
15 interlace method) and a scanning method in which a scanning selection signal is applied to non-adjacent scanning electrodes in at least two consecutive field scans, the surface temperature of the liquid crystal display element is 40 ° C., and display is performed on the entire surface of the element. The possible driving voltage Vop and the drivable area for one line scanning time 1H were measured. FIG. 4 is a graph showing a result of the measurement, and a drivable region is between two straight lines.

According to the above result, the driving voltage Vop is 10
When V, 1H (horizontal scanning time) is 120 to 130 μs
c, when the driving voltage Vop is 20 V, 1H is 45 to 60 μ
sec. Since the number of scanning electrodes of the liquid crystal display element used in this embodiment is 480, the frame frequency is about 17 Hz when the driving voltage Vop = 10 V, and the frame frequency is about 40 Hz when Vop = 20 V.

Under the conditions within the drivable area, a schematic pattern of cursor movement as shown in FIG. 5 is displayed, and the cursor is sequentially moved from the top to the bottom of the panel as shown by arrow B in FIG. A test was performed in which the positive display and the negative display were repeated every time, and the visibility and durability of the moving cursor were confirmed. In this case, the frame display was always white.

The ratio of the time the cursor is moving to the time the cursor is stopped is about 1: 1.

In the display pattern shown in FIG. 5, the conditions of Vop = 20 V, 1H = 52 μsec, and frame frequency = 40 Hz are set when the cursor is moved and when negative or positive reversal is performed, that is, when the display is rewritten. When not changing, Vop = 10V, 1H = 12
As a condition of 5 μsec, frame frequency = 17 Hz,
The visibility of the moving cursor and the durability for a predetermined time were confirmed.

As a result, good results were obtained in both visibility and durability, and a result that there was no practical problem as a display device was obtained.

Comparative Example 1 In the display pattern shown in FIG. 5, Vop = 10 V, 1H = 125 μs both when the screen is updated and when the screen is not updated.
c, the visibility of the moving cursor and the durability for a predetermined time were confirmed under the conditions of the frame frequency = 17 Hz as in the example.

As a result, although the durability was good, a phenomenon in which the display at the time of moving the cursor appeared to be uneven due to the low frame frequency occurred, which was a problem in practical use.

Comparative Example 2 In the display pattern shown in FIG. 5, Vop = 20 V, 1H = 52 μs both when the screen is updated and when the screen is not updated.
c, under the condition that the frame frequency was 40 Hz, the visibility of the moving cursor and the durability for a predetermined time were confirmed in the same manner as in the example. As a result, in contrast to Comparative Example 1, good results were obtained in the visibility at the time of updating the screen. After the endurance, a part 61 of the frame display part on the upper part of the display element as shown in FIG.
The phenomenon that 62 was colored yellow was observed. this is,
Since the frame display is always fixed at white, the liquid crystal molecules move,
This is due to the increased cell thickness. Therefore, as in Comparative Example 1, there was a problem in practical use.

[0028]

As described above, according to the present invention, the driving conditions are set so that the frame frequency becomes faster when the screen display is updated, and if the image display is not updated, the frame frequency is reduced. By performing the drive control, it is possible to realize a display device having practically no problem in both visibility and durability of a moving image.

[Brief description of the drawings]

FIG. 1 is a plan view of a ferroelectric liquid crystal display device according to one embodiment of the present invention.

FIG. 2 is a plan view of an electrode of the liquid crystal display element used in FIG.

FIG. 3 is a driving voltage waveform diagram used for driving the liquid crystal element of FIG.

4 is a diagram showing a relationship between a driving voltage and a one-line scanning time when the display element shown in FIG. 1 is driven using the driving voltage waveform of FIG.

FIG. 5 is a display pattern diagram used in Examples and Comparative Examples.

FIG. 6 is a plan view of a liquid crystal element after a durability test of Comparative Example 2.

[Explanation of symbols]

1: Ferroelectric liquid crystal display element, 2: Driver IC board for scanning electrode, 3: Driver IC board for information electrode, 1
1: glass substrate, 12: sealing part, 13: sealing part, 14:
Information display area, 15: frame display area, S ₁ , S ₂ , ‥‥,
S _m: scanning _{electrodes, I 1, I 2, ‥‥} , I n: data electrodes.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Special Table Hei 5-508244 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 505-580 G09G 3/36

Claims (3)

(57) [Claims] 1. A display device comprising a ferroelectric liquid crystal display element and driving means for driving the liquid crystal display element, wherein a detection is performed for detecting that image information to be displayed on the liquid crystal display element has been changed. Means, when the image information to be displayed on the liquid crystal display element is changed according to the detection result from the detection means, so that the frame frequency is higher than when the image information is not changed, Means for changing driving conditions of the liquid crystal display element. 2. The method according to claim 1, wherein the driving condition is changed by setting two kinds of frame frequencies as the driving condition, and the detecting unit changes the image information to be displayed on the liquid crystal display element. Is detected, the liquid crystal display element is driven at the higher frame frequency until the display image on the liquid crystal display element is updated to the changed image, and the other frame frequency is lower. The display device according to claim 1, further comprising: a driving unit. 3. A method of driving a display device having a ferroelectric liquid crystal display element and a driving means for driving the liquid crystal display element, wherein a change is made to image information to be displayed on the liquid crystal display element. Detecting, changing the frame frequency according to the detection result, and changing the driving condition so that the frame frequency is increased when the image information to be displayed on the liquid crystal display element is changed, and changing the image information to the image information. Wherein the driving condition is changed such that the frame frequency is lower than when the image information is changed, when the image information is not changed.